The present invention relates broadly to a diagnostic catheter utilized in urodynamic investigations to detect and to evaluate in quantitative terms constrictions that might exist along the urethral duct of a human or animal subject. The urethral pressure profile test is now commonly used in the assessment of urodynamic evaluation. This test is especially pertinent with respect to patients with incontinence or obstructive symptomatology. Usually a profile of urethral pressure may be obtained by the withdrawal of a pressure recording catheter from the bladder through the urethra. Several methods of profilometry exist including measurement of pressure inside of a balloon which traverses the urethra and also the measurement of the urethral pressure that is transmitted against a fluid or gas that is infused through a small catheter traversing the urethra. Utilizing the last technique, single and multi-channeled urodynamic catheters employ an open system in the sense that pressures are measured by passing a liquid or gas through the catheter and then out through one or more of the orifices. Depending on the size of the space between the catheter and the urethral wall, flow is restricted to a certain degree and pressure will vary as the catheter is withdrawn. Liquid or gas will keep flowing through and out during the entire procedure. Normally, water is infused at the rate of 2 cc/min. As the catheter enters the urethral canal, it registers a minimal rise in pressure at the level of the internal sphincter or bladder neck. Proceeding downward, pressure will increase and reach a peak generally at the midpoint of the urethra in the female and in the membranrous urethra in the male, and then it will progressively drop.
What are known in the art as membrane catheters are closed systems also used in obtaining urethral pressure profiles. Here, the liquid that enters the catheter under pressure serves to expand a thin balloon or elastic element which is located adjacent the end of the catheter. The fluid is captive in the balloon and cannot flow out of the catheter. Single or double membrane catheters are frequently used for recording such urethral pressure profiles. As they are manually or mechanically withdrawn from the bladder cavity, the balloons will traverse the entire length of the urethra and serve to transmit pressure through the liquid with which they are inflated back to a chart recorder or other type of recording device. Frequently, pressure profiles are obtained under various states of stress such as coughing or bearing down and voluntary contraction of muscles. It will be obvious that any internal obstruction such as a tumor or other constriction along the urethra will oppose the expansion of the elastic balloon element. The back pressure that is created is therefore measured and recorded as noted.
A comparison of these various methods of recording urethral pressure profile may be found in the paper of Schmidt et al. "Recording Urethral Pressure Profile, Comparison of Methods and Clinical Implications," Urology, October 1977, Vol. X, No. 4, pp. 390-7.
Another test that is frequently performed in urodynamic investigations is the cystometrogram (CMG). This is a test of detrusor muscle function and consists of distending the bladder with a known volume of a fluid or gas while recording the intravesical pressure. In performing this test, the bladder can be filled with either water, saline solution, air or carbon dioxide or the like. The medium can be instilled either through the urethra or suprapubically. In most cases, the medium is instilled through a double lumen catheter at a rate of approximately 10 cc/min. The catheter that is employed permits both filling of the bladder and recording of bladder pressure.
In a normal CMG test the filling phase looks at the bladder's ability to comply to increased volume. The detrusor muscle normally expands as volume increases so that the bladder initially rises very little in pressure to the time the patient voids. If bladder pressure continually rises during filling, it can be due to a number of factors which would bear further investigation. Another important observation during the filling phase of the CMG is any rise in bladder pressure that is not accompanied by rise in abdominal pressure. This represents detrusor contraction. The voiding phase of a CMG determines if detrusor reflex exists.
Frequently, CMG testing and urethral pressure profile tests are performed in sequence wherein the CMG test determines bladder capacity and pressure and subsequently a urethral pressure profile test is performed utilizing a membrane catheter.
An example of a urethral membrane catheter of the type known in the art today is the dual channel membrane catheter produced by Brown Corporation of Santa Barbara, Calif. This catheter is designed to profile the dynamic and/or static pressure of the urethra and a second channel is provided for simultaneously recording intravesical pressure while profiling the urethra. The catheter is constructed of silicone and is barium impregnated for X-ray detection. A membrane chamber is located approximately 8 cm from the distal end and when infused with carbon dioxide at controlled flow rates, serves to measure the total urethral resistance against the membrane. Static urethral pressure is measured by placing the membrane chamber at the point in the urethra where greatest resistance is measured while infusing the bladder with carbon dioxide on the second channel. It should be noted that the membrane of the type utilized in the Brown catheter and others well-known in the art are in the form of sleeves which expand to form a small balloon such as found in the conventional Foley catheter. Examples of Foley type catheters may be seen in U.S. Pat. Nos. 3,825,013 and 3,528,869.
The invention herein described is referred to as a disc membrane catheter and varies from the prior art in that the elastic elements are applied in the form of a thin silicone or other elastic disc which is applied over one or more small oblong openings in the catheter shaft. Application of internal pressure through the catheter causes these flat disc membranes to expand outwardly. Because they are dimensionally much smaller than the balloon membranes, the disc-type yields better resolution with respect to location of constrictions or obstructions along the urethra.
While in many measurement situations, the external resistant pressure is applied evenly, in some instances, and especially along the urethral duct, there may be an obstruction present in a small localized area only along one side of the urethra. A circular balloon type membrane would not be useful in detecting the orientation of such an obstruction. However, the disc membrane of the present invention normally responds to pressure averaged around the catheter. When a discontinuity is present, however, its location can be detected by rotating the catheter between forward and backward passes. In this respect, the disc membrane is much more versatile than the balloon type described above.
An important advantage of the disc membrane catheter over the conventional membrane type is its relative freedom from entrapped air bubbles. During the filling process the conventional balloon type membrane invariably will trap large air bubbles in the expanding balloon. Such air bubbles being compressible interfere with the accuracy of the pressure readings when the catheter is in use. Elaborate and time consuming procedures are required to dislodge the bubbles and avoiding them is nearly impossible. The disc membrane catheter's basic geometry is such that it does not provide large corners in which the air bubbles can remain lodged.